1. Technical Field
This disclosure relates generally to an engine control system which may be employed in automotive vehicles and is designed to use an algorithm to control operations of actuators such as a fuel injector and an EGR (Exhaust Gas Recirculation) valve to regulate a combustion state of fuel in an internal combustion engine and also to control the performance of the engine.
2. Background Art
Engine control systems are known which determine controlled variables or parameters such as the quantity of fuel to be injected into an engine (which will also be referred to as an injection quantity), the injection timing, the amount of a portion of exhaust gas to be returned back to the inlet of the engine (which will also be referred to as an EGR amount below), the boost pressure, the amount of intake air, the ignition timing, and an open/close timing of intake and exhaust valves to yield desired engine performance. As parameters related to the engine performance (which will also be referred to below as performance parameters), there are the amount of exhaust emissions, for example, NOx or CO, the torque outputted by the engine, and the specific fuel consumption (or fuel efficiency).
Most of the engine control systems are equipped with control maps which store optimum values of the controlled parameters, for example, the quantity of fuel to be injected into the engine, etc. for achieving the desired engine performance. The control maps are usually made by adaptability tests performed by an engine manufacturer. The engine control systems work to calculate a target value (which will also be referred to as a command) of each of the controlled parameters needed to meet the desired engine performance using a corresponding one of the control maps and output the command to a corresponding actuator to bring the value of the performance parameter into agreement with its target value.
When the commands of the controlled parameters are set up independently of each other, it may result in interference between the different types of controlled parameters in that when one of the performance parameters reaches its target value, another performance parameter deviates from its target value, while when the another performance parameter is brought to the target value, the previously mentioned one of the performance parameters deviates from the target one. It is, therefore, very difficult to bring the different types of performance parameters into agreement with target values simultaneously.
Japanese Patent First Publication No. 2008-223643 teaches an engine control system which calculates a target value of each combustion parameter (e.g., a target pressure in a cylinder of the engine) based on an operating condition of the engine and brings an actual value of the combustion parameter, as measured by a sensor, into agreement with the target value in a feedback mode. Japanese Patent First Publication No. 2007-77935 teaches a feedback mode using a predicted value, as calculated by a simulation model.
The above prior art systems are designed to determine a target value of each of the combustion parameters as functions of the respective performance parameters such as the amount of exhaust emissions, the torque outputted by the engine, and the specific fuel consumption. Therefore, when an actual value of one of the combustion parameters is brought into agreement with the target value in the feedback mode, a corresponding one of the performance parameters will be adjusted to its target value, but however, it may result in a deviation of another of the performance parameters from the target value thereof. It is, thus, difficult to bring the different types of performance parameters into agreement with target values simultaneously.